The extracellular matrix (ECM) plays an important role in vascular tissue structure, maintenance, and function. Lysyl oxidases catalyze a key step in the posttranslational cross-linking of elastin and collagens in the ECM. Gene knockout studies in mice suggested a role for lysyl oxidase-like (LOXL1) in adult elastin synthesis and a role for its isoform, lysyl oxidase (LOX), in the synthesis of both collagens and elastin during development. However, the relative expression of both isoforms as a function of age is not known and was therefore investigated here. LOX and LOXL1 immunohistochemistry and real-time RT-PCR were performed during development, growth and aging in the aorta of LOU and Brown-Norway (BN) rats, two inbred strains with different susceptibilities to arterial fragility. In addition, expression of genes encoding for elastic fiber proteins and type I collagen, together with elastin and collagen contents, was measured in adult and old rat aortas. High aortic LOX expression was observed early in the development (embryonic day 15), followed by a drastic reduction in adulthood, whereas LOXL1 was mainly detectable in the intima and media; its expression was maintained throughout life in the LOU rat. Expression of tropoelastin, type-I collagen, and LOXL1 genes was reduced in the aorta of 6-week-old BN rats. Aging is characterized by a decreased elastin/collagen ratio and a greatly decreased expression of LOX, tropoelastin, and type-I collagen. These findings indicate a different spatial and temporal expression of LOX and LOXL1 during growth and aging in the rat aorta and suggest specific roles for LOX and LOXL1 in the synthesis and remodeling of elastic and collagen fibers.
H aploinsufficiency of elastin in patients with WilliamsBeuren syndrome leads, in more than half of cases, to development of supravalvular aortic stenosis and hypertension.1 Moreover, Eln +/− mice, a model for supravalvular aortic stenosis disease, have a higher arterial pressure (∆25-30 mm Hg) than their wild-type counterparts.2 These cardiovascular features are clearly linked to the decreased elastin synthesis in the aorta during development. Thus, it would be of interest to find molecules able to enhance elastin synthesis to treat this condition.We previously showed that the Brown Norway (BN) rat, a normotensive inbred strain, presents the lowest content of elastin in the aorta compared with 6 other inbred rat strains. [3][4][5] We also demonstrated that, compared with the LOU rat, the elastin deficit in the thoracic aorta of the BN rat is partly caused by a decrease in the synthesis of tropoelastin (TE), the soluble precursor of elastin. However, elastin gene polymorphism accounts for only 3.9% of the elastin content variance in F2 BNxLOU rats.4 After a genome-wide search for quantitative trait loci influencing the aortic elastin content in an F2 population derived from BN and LOU rats, we identified on chromosomes 2 and 14, 3 quantitative trait loci specifically controlling elastin levels: Ael1, Ael2, and Ael3. 6 The polymorphic marker, D2Wox26, corresponding to the maximum logarithm of odds score value of Ael2, is situated within the gene encoding for the Na + /K + -ATPase α1 subunit. In addition, several other genes encoding for potassium channels are contained in Ael1 (Kcnmb2, Hcn1) and Ael2 (Hcn3, Kcnn3, Kcnd3, Kcna2, Kcna3, and Kcna10). This result supports the hypothesis that the deficit of aortic elastin content in the BN rat could be explained by anomalies in intracellular potassium concentration ([K + ] i ).Abstract-Hypertension is a cardiovascular disorder that appears in more than half of the patients with Williams-Beuren syndrome, hemizygous for the elastin gene among 26 to 28 other genes. It was shown that the antihypertensive drug minoxidil, an ATP-dependent potassium channel opener, enhances elastic fiber formation; however, no wide clinical application was developed because of its adverse side effects. The Brown Norway rat was used here as an arterial elastin-deficient model. We tested 3 different potassium channel openers, minoxidil, diazoxide, and pinacidil, and 1 potassium channel blocker, glibenclamide, on cultured smooth muscle cells from Brown Norway rat aorta. All tested potassium channel openers increased mRNAs encoding proteins and enzymes involved in elastic fiber formation, whereas glibenclamide had the opposite effect. The higher steady-state level of tropoelastin mRNA in minoxidil-treated cells was attributable to an increase in both transcription and mRNA stability. Treatment of Brown Norway rats for 10 weeks with minoxidil or diazoxide increased elastic fiber content and decreased cell number in the aortic media, without changing collagen content. The minoxidil-induced card...
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